162.6 mJ high-energy and high-efficiency KTP optical parametric oscillator at 2 µm

A high-energy and high-efficiency 2 m nanosecond optical parametric oscillator (OPO) with excellent energy stability is reported.The cavity adopts a plane-plane configuration with two potassium titanyl phosphate (KTP) crystals inserted using a spatial walk-off compensated orientation.The KTP-OPO is pumped by a 1064 nm Nd:YAG Q-switched laser at a repetition rate of 10 Hz and produces a maximum pulse energy of 162.6 mJ at a pump energy of 431 mJ, corresponding to an optical conversion efficiency of 37.7% and a slope efficiency of 45.2%.The energy stability shows a record root mean square (RMS) of 0.4% over 30 min.To our knowledge, this represents the highest 2 m pulse energy achieved via the 1 m laser-pumped KTP-OPO scheme, which could be an excellent laser source for driving extreme ultraviolet (EUV) radiations in the subsequent demonstration experiments.